Optical recording discs of the write-once or rewriteable type include a substrate having a recording layer. The substrate is formed by injection molding to include a wobbled groove on the surface of the substrate where the recording layer is formed. The groove defines recording channels on the disc for recording data and also provides for tracking of the disc while writing or reading data. The groove, which is a frequency modulated signal after detection and processing, also contains addressing and other information that are necessary for the write and read processes. The groove is usually in accordance with Orange Book standards. "Orange Book" is a licensed specification published by Philips Corporation and Sony Corporation which defines key properties of recordable compact disc (CD-R) media and recording procedures.
The recording layer, which can include an organic dye, is deposited on the substrate so as to completely cover the groove. The recording layer can be deposited by various techniques, including spin-coating, gravure, roller, flexographic, and vapor phase deposition. A reflective layer is then formed over the entire recording layer using similar techniques. The reflective layer can be, for example, gold, silver, or copper.
Because the reflective layer does not adhere well to the deposited recording layer, the outer region of the substrate must be substantially free of the recording layer to ensure proper adhesion of the reflective layer to the substrate. However, during deposition of the recording layer, the outer region of the substrate becomes wholly or partially coated with a residual portion of the recording layer. Consequently, the residual portion of the recording layer must be removed from the outer region of the substrate prior to deposition of the reflective layer. In a manner well known in the art, a dye compatible solvent is directed onto the outer region of the rotating disc to dissolve and remove the residual portion of the recording layer from the substrate. However, during evaporation and drying of the solvent, a portion of the recording layer uncontrollably bleeds outward toward the outer peripheral edge of the disc and forms undesirable corrugations at the outermost region of the substrate. The corrugations, which can extend for approximately one to three millimeters from the desired outer edge of the recording layer toward the outer edge of the substrate, substantially reduce the adhesion of the reflective layer to the substrate, as well as result in a deteriorated appearance of the recording layer. Poor adhesion reduces the durability, and thus, the useful lifetime of the disc. Additional application of solvent does not eliminate the corrugations.
In addition, as the solvent is spun onto the substrate to remove the residual portion of the recording layer, a portion of the solvent wicks under the outer edge of the recording layer, causing the recording layer to be lifted from the substrate. As the solvent evaporates, the recording layer is redeposited onto the substrate in a nonuniform manner so that a bead of dye is formed on the substrate at the outermost edge of the recording layer. This edge bead is a weakness in the optical disc, causing delamination of the layers when the disc is subjected to physical abrasion during either manufacturing or subsequent usage of the disc. Thus, the edge bead further decreases the durability and useful lifetime of the disc. Furthermore, during application of the solvent, a containment apparatus is typically used to partially surround the disc and contain any solvent droplets which are formed during the cleaning process and could become redeposited onto the recording layer. These droplets cause recording layer defects, sometimes referred to as dropouts, which decreases the quality of the recorded data and could result in an unusable disc.
In order to provide sufficient cleaning of the substrate prior to deposition of the reflective layer, it is necessary to utilize a solvent having physical properties compatible with the recording dye and substrate materials. The choice of solvents becomes limited and potentially costly, and the cleaning time is increased because of the inefficiency of the available solvents. In addition, many of the available solvents can cause environmental damage.